Plastics such as polypropylenes, polyethylenes and poly(vinyl chloride)s derived from fossil resources such as petroleum, are molded typically into food packaging films, electric appliances and industrial materials and are very important materials essential for our livelihood. It is, however, well known that these plastics are not biodegradable, thereby remain in the nature semipermanently after their use, significantly affect an ecosystem, and lead to destruction of environment in various ways.
Under these circumstances, biodegradable resins have received attention. Among them, biodegradable resins prepared from plants (vegetables), namely, plant-derived biodegradable resins are to be used as replacements from fossil resource-derived non-biodegradable plastics. In particular, poly(lactic acid) resins have recently received attention and have been produced increasingly. They have received attention for the following reasons. Social demands have been made on providing cycling systems of matter in which limited fossil resources are saved and thoroughly reused as resources. Under these circumstances, plastics derived from fossil resources are considered to be remarkably out of the cycling systems of matter. In contrast, poly(lactic acid)s are expected to constitute cycling systems of matter, in which the poly(lactic acid)s are recycled as resources, because they are prepared from saccharides derived from plants such as corn and potatoes, or lactic acid as fermented products of such saccharides.
Materials for poly(lactic acid) resins are synthetically prepared from saccharides derived from grains which are recycling capable resources such as corn and potatoes, or lactic acid as fermented products of such saccharides. In addition, poly(lactic acid) resins which become unnecessary are easily hydrolyzed in natural environments and decomposed by the action of microorganisms and ultimately become water and carbon dioxide gas.
Films, sheets, and other molded resinous articles including biodegradable resins such as poly(lactic acid) resins are known to exhibit performance equivalent to that of conventional plastics. Among them, poly(lactic acid) resins have very high transparency and are very usable in packaging uses in which transparency is an important factor. In addition, they have water vapor permeability equal to or better than that of conventional oriented polypropylene (OPP) or oriented polystyrene (OPS) films and are expected to replace these films.
As is described above, biodegradable resins have many advantages and are applicable to molded articles such as films and sheets. However, since they have electrical insulating properties typical to resins, they are very susceptible to being electrically charged as in regular resins, and thereby they have various problems due to electrical charges. Such problems include, for example, crawling of ink upon printing, flying out of contents to be packaged upon packaging, and dust adhesion to products to impair appearance of the products.
Biodegradable resins also have problems caused by low hydrophilicity typical to plastics. For example, films for food packaging should have transparency so as to see the appearance of food packaged therein, but the surfaces of such films become fogged due to water drops derived from water vapor from the food.
To solve these problems, a kneading process of previously adding a surfactant to a resin has been employed. According to the kneading process, the surfactant bleeds out from the inside to the surface of the resulting molded article to form a surfactant layer, and thereby exhibits performance such as antistatic properties and antifogging properties. These properties may sustain to some extent even when the surfactant at surface is wiped off, because the surfactant in the inside of the resin bleeds out again to thereby recover the properties. As is described above, the performance is exhibited as a result of bleedout of the surfactant from the resin according to the kneading process. However, the degree of bleedout is believed to vary significantly depending on the crystallinity of the resin, such as degree of crystallization and degree of orientation of crystals, and the compatibility (miscibility) between the resin and the surfactant. Among such factors, the crystallinity of the resin and the compatibility of the surfactant also significantly affect the appearance of the resin.
Patent Document 1 demonstrates that a polyhydric alcohol and a fatty acid ester thereof are incorporated into a poly(lactic acid) resin to provide antistatic films and sheets. Patent Document 2 describes that antistatic properties are imparted to a poly(lactic acid) by containing a nonionic surfactant including a glycerol fatty acid ester. Patent Document 3 shows that antistatic properties are imparted to a caprolactone resin as a biodegradable resin by containing a nonionic surfactant including a glycerol fatty acid ester. Patent Document 4 demonstrates that antistatic properties are exhibited while suppressing deterioration in transparency due to an alkylsulfonate salt by containing an alkylsulfonate salt of a nonionic surfactant in combination with a polyhydric alcohol or a fatty acid alkylolamide compound. The resulting resins prepared according to these techniques, however, do not have practically sufficient antistatic properties yet. Such surfactants having poor compatibility with resins also markedly affect the appearance of the resins and, in particular, significantly impair the transparency of poly(lactic acid)s that are featured by transparency.                Patent Document 1: Japanese Patent Application Laid-open No. Hei 9-221587 (pages 1 to 9)        Patent Document 2: Japanese Patent Application Laid-open No. Hei 10-36650 (pages 1 to 14)        Patent Document 3: Japanese Patent Application Laid-open No. 2002-60603 (pages 1 to 5)        Patent Document 4: Japanese Patent Application Laid-open No. 2003-261757(pages 1 to 6)        Patent Document 5: Japanese Patent Application Laid-open No. Hei 9-278936(pages 1 to 14)        